U.S. Pat. No. 4,009,702 discloses a combustion chamber of penta-roof design, wherein combustion occurs substantially within a main cavity formed with vertical walls within the piston. A series of circular recesses formed in the piston face facilitate intermixing of air with injected fuel and allow gas and air spill over from the main cavity to provide additional combustion during high engine load conditions.
In U.S. Pat. No. 2,213,202, a restricted combustion chamber of an ellipsoidal shape is provided in an internal combustion engine by valve discs of two telescoped valves arranged coaxially with a piston chamber and cylinder of the engine, and an annular projection on the piston face.